The frequency-weighted measurement has been extended by a gating function. The EBU PLOUD- Group developed a gating function to exclude quiet sections from the measurement to prevent possible loudness underread. Examples are background noise and atmo, which do not add to the loudness perception as much as louder signals do.
This gating function consists of an absolute threshold at -70LUFS and a relative threshold 10LU below the absolute-gated level. This involves the necessity to recalculate the whole measurement with every subsequent block. The ITU approved the gating function and included it into its recommendations ITU-R BS. 1770-2 and later.
Important note! Systems working in ITU 1770-1 mode do not feature a gating function. Thus its output readings may vary a bit from meters compliant to EBU R128 or ITU 1770-2/-3. Further keep in mind that the gate is only applicable to the integrated or program loudness measurement (from start to stop) and not used for short-term or momentary measurements.